diff options
| -rw-r--r-- | libc/sysdeps/linux/xtensa/setjmp.S | 150 |
1 files changed, 86 insertions, 64 deletions
diff --git a/libc/sysdeps/linux/xtensa/setjmp.S b/libc/sysdeps/linux/xtensa/setjmp.S index aac27406c..bf4691294 100644 --- a/libc/sysdeps/linux/xtensa/setjmp.S +++ b/libc/sysdeps/linux/xtensa/setjmp.S @@ -24,24 +24,52 @@ then sets things up so that it will return to the right place, using a window underflow to automatically restore the registers. - Note that it would probably be sufficient to only copy the - registers from setjmp's caller into jmp_buf. However, we also copy - the save area located at the stack pointer of setjmp's caller. - This save area will typically remain intact until the longjmp call. - The one exception is when there is an intervening alloca in - setjmp's caller. This is certainly an unusual situation and is - likely to cause problems in any case (the storage allocated on the - stack cannot be safely accessed following the longjmp). As bad as - it is, on most systems this situation would not necessarily lead to - a catastrophic failure. If we did not preserve the extra save area - on Xtensa, however, it would. When setjmp's caller returns after a - longjmp, there will be a window underflow; an invalid return - address or stack pointer in the save area will almost certainly - lead to a crash. Keeping a copy of the extra save area in the - jmp_buf avoids this with only a small additional cost. If setjmp - and longjmp are ever time-critical, this could be removed. */ + Note that we also save the area located just below the stack pointer + of the caller. This save area could get overwritten by alloca + following the call to setjmp. The alloca moves the stack pointer + to allocate memory on the stack. This newly allocated memory + includes(!) the original save area (alloca copies the save area + before it moves that stack pointer). + + + previous caller SP -> |------------------------------| <-----+ + | caller-2 registers a0-a3 | | p + |------------------------------| | o + | caller registers a4-a8/a12 | | i + |------------------------------| | n + | caller local stack | | t + caller SP -> |------------------------------| <-+ | s + | caller-1 registers a0-a3 | -:---+ + callee (setjmp) SP -> |==============================| | + | caller registers a0-a3 | --+ + |------------------------------| + + In case of an alloca, registers a0-a3 of the previous caller (caller-1) + are copied (*), and the original location get likely overwritten. + + previous caller SP -> |------------------------------| <-----+ + | caller-2 registers a0-a3 | | p + |------------------------------| | o + | caller registers a4-a8/a12 | | i + |------------------------------| | n + | caller local stack | | t + caller SP before alloca-> |------------------------------| | s + | alloca area (overwrites old | | + | copy of caller-1 registers) | | + caller SP after alloca -> |------------------------------| <-+ | + | caller-1 registers a0-a3 (*) | -:---+ + callee (setjmp) SP -> |==============================| | + | caller registers a0-a3 | --+ + |------------------------------| + + So, when longcall returns to the original caller SP, it also needs + to restore the save area below the SP. + + */ #include "sysdep.h" + +/* NOTE: The ENTRY macro must allocate exactly 16 bytes (entry a1, 16) */ /* int setjmp (a2 = jmp_buf env) */ @@ -56,8 +84,7 @@ ENTRY (setjmp) j 1f END (setjmp) -/* int __sigsetjmp (a2 = jmp_buf env, - a3 = int savemask) */ +/* int __sigsetjmp (a2 = jmp_buf env, a3 = int savemask) */ ENTRY (__sigsetjmp) 1: @@ -65,61 +92,56 @@ ENTRY (__sigsetjmp) movi a4, __window_spill callx4 a4 - /* Preserve the second argument (savemask) in a15. The selection - of a15 is arbitrary, except it's otherwise unused. There is no - risk of triggering a window overflow since we just returned - from __window_spill(). */ - mov a15, a3 - - /* Copy the register save area at (sp - 16). */ - addi a5, a1, -16 - l32i a3, a5, 0 - l32i a4, a5, 4 - s32i a3, a2, 0 - s32i a4, a2, 4 - l32i a3, a5, 8 - l32i a4, a5, 12 - s32i a3, a2, 8 - s32i a4, a2, 12 - - /* Copy 0-8 words from the register overflow area. */ - extui a3, a0, 30, 2 - blti a3, 2, .Lendsj - l32i a7, a5, 4 - slli a4, a3, 4 - sub a5, a7, a4 - addi a6, a2, 16 - addi a7, a7, -16 /* a7 = end of register overflow area */ + /* Copy the caller register a0-a3 at (sp - 16) to jmpbuf. */ + addi a7, a1, -16 + l32i a4, a7, 0 + l32i a5, a7, 4 + s32i a4, a2, 0 + s32i a5, a2, 4 + l32i a4, a7, 8 + l32i a5, a7, 12 + s32i a4, a2, 8 + s32i a5, a2, 12 + + /* Copy the caller registers a4-a8/a12 from the overflow area. */ + /* Note that entry moved the SP by 16B, so SP of caller-1 is at 4(sp) */ + extui a7, a0, 30, 2 + blti a7, 2, .Lendsj + l32i a8, a1, 4 /* a8: SP of 'caller-1' */ + slli a4, a7, 4 + sub a6, a8, a4 + addi a5, a2, 16 + addi a8, a8, -16 /* a8: end of register overflow area */ .Lsjloop: - l32i a3, a5, 0 - l32i a4, a5, 4 - s32i a3, a6, 0 - s32i a4, a6, 4 - l32i a3, a5, 8 - l32i a4, a5, 12 - s32i a3, a6, 8 - s32i a4, a6, 12 - addi a5, a5, 16 + l32i a7, a6, 0 + l32i a4, a6, 4 + s32i a7, a5, 0 + s32i a4, a5, 4 + l32i a7, a6, 8 + l32i a4, a6, 12 + s32i a7, a5, 8 + s32i a4, a5, 12 + addi a5, a6, 16 addi a6, a6, 16 - blt a5, a7, .Lsjloop + blt a6, a8, .Lsjloop .Lendsj: - /* Copy the register save area at sp. */ - l32i a3, a1, 0 - l32i a4, a1, 4 - s32i a3, a2, 48 - s32i a4, a2, 52 - l32i a3, a1, 8 - l32i a4, a1, 12 - s32i a3, a2, 56 - s32i a4, a2, 60 + /* Copy previous caller registers (this is assuming 'entry a1,16') */ + l32i a4, a1, 0 + l32i a5, a1, 4 + s32i a4, a2, 48 + s32i a5, a2, 52 + l32i a4, a1, 8 + l32i a5, a1, 12 + s32i a4, a2, 56 + s32i a5, a2, 60 /* Save the return address, including the window size bits. */ s32i a0, a2, 64 - /* a2 still addresses jmp_buf. a15 contains savemask. */ + /* a2 still points to jmp_buf. a3 contains savemask. */ mov a6, a2 - mov a7, a15 + mov a7, a3 movi a3, __sigjmp_save callx4 a3 mov a2, a6 |